minor #2939 [Icons] Fix icon_sets configuration documentation, follow #2938 (Kocal)

This PR was merged into the 2.x branch.

Discussion
----------

[Icons] Fix `icon_sets` configuration documentation, follow #2938

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no <!-- please update src/**/CHANGELOG.md files -->
| Docs?         | yes <!-- required for new features -->
| Issues        | Fix #... <!-- prefix each issue number with "Fix #", no need to create an issue if none exist, explain below instead -->
| License       | MIT

<!--
Replace this notice by a description of your feature/bugfix.
This will help reviewers and should be a good start for the documentation.

Additionally (see https://symfony.com/releases):
 - Always add tests and ensure they pass.
 - For new features, provide some code snippets to help understand usage.
 - Features and deprecations must be submitted against branch main.
 - Update/add documentation as required (we can help!)
 - Changelog entry should follow https://symfony.com/doc/current/contributing/code/conventions.html#writing-a-changelog-entry
 - Never break backward compatibility (see https://symfony.com/bc).
-->

Following #2938

Commits
-------

f5884b3 [Icons] Fix `icon_sets` configuration documentation, follow #2938

Author: Kocal

src/Icons/doc/index.rst

@@ -632,9 +632,10 @@ Full Configuration
         icon_sets:
             # Icon set for "flags", can be used like this: ux_icon('flags:fr')
             flags:
-                It can either be mapped to a local directory...
+                # It can either be mapped to a local directory...
                 path: '%kernel.project_dir%/assets/images/flags'
-                ... or to an existing icon set identifier
+
+                # ... or to an existing icon set identifier
                 alias: 'lucide'
 
                 # Override the default attributes (default_icon_attributes) for this icon set